20 mg/kg
A structural baseline
20 ppm by mass equals 20 milligrams per kilogram. It is often the sweet spot for structural and shielding components where extreme purity is less critical.
Graphite purity decision guide
Evaluate a 20 ppm ash target for your component location, balancing purity requirements with cost-effective sourcing.
20 mg/kg
20 ppm by mass equals 20 milligrams per kilogram. It is often the sweet spot for structural and shielding components where extreme purity is less critical.
Cost vs. Purity
Specifying 5 ppm or 10 ppm for outer heat shields can add unnecessary cost. 20 ppm typically prevents gross contamination efficiently.
Element specific
At 20 ppm, understanding which elements make up that residue becomes more important, especially for elements like Boron, Iron, or Vanadium.
01 · Define
Identify if the component is in the inner hot zone or serves as an outer shield. 20ppm is often adequate for the latter.
02 · Measure
Request total ash along with specific limits for elements detrimental to your process, ensuring they don't dominate the 20ppm residue.
03 · Qualify
Verify that the 20ppm limit is reliably met across lots, especially if you are downgrading from a higher purity specification.
A single 20 ppm ash number is a good starting point, but you need to confirm the test method and element breakdown for critical processes.
| Question | Ask for | Why it matters |
|---|---|---|
| What is the primary composition of the 20ppm ash? | A typical element breakdown or GDMS scan. | 20ppm of benign elements (like Silicon) acts very differently than 20ppm of transitional metals (like Iron). |
| Which contaminants are controlled? | A process-defined element list with result, method, and detection or quantitation limit. | A total ash value cannot show whether a specific impurity is below its own limit. |
| Does the report cover this order? | Lot or batch identifier and a traceable link to the quoted grade and part. | A typical or historical result may not describe the material being delivered. |
| What does the result not prove? | Outgassing characteristics under vacuum or specific thermal cycles. | Material screening does not replace qualification in the buyer’s furnace and process. |
In many high-temperature processes, contamination risk drops exponentially with distance from the melt or growth interface. For outer thermal shielding, heating elements, and structural supports, 20ppm ash graphite often provides identical functional performance to 5ppm grades while significantly reducing material costs.
However, for inner crucibles in SiC sublimation growth or direct contact components in epitaxy, evidence suggests volatile impurities from a 20ppm baseline may incorporate into the crystal, unless those impurities are specifically proven benign for the given recipe.
Evidence checked 2026-09-28. Standard summaries and published studies do not specify your acceptance limits; verify the current method revision and qualification scope with your lab and supplier.
It depends on the component. It is generally not pure enough for direct contact crucibles, but often perfectly suitable for structural supports and outer shielding.
No. It is a total residue target. Request separate limits and results for elements that matter to your process.
For a mass fraction, yes. Confirm whether the report uses a mass basis and whether results are reported on a dry or other agreed sample basis.
Prices vary widely, but halogen-purified <5ppm graphite commands a significant premium over standard 20ppm to 50ppm grades due to the extra processing time and hazardous gases involved.
Not automatically. Ask which sample and processing stage the report represents, and agree how it relates to the delivered part and lot.
Sometimes. A coating on a 20ppm substrate may seal in impurities, but coating integrity, thermal expansion match, and furnace qualification remain critical checks.
Send the component drawing, process conditions, ash target, element limits, and report expectations. Engineering can review if a 20ppm grade is appropriate for your specific component location.
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Attach DWG, STEP, or PDF drawings and include purity, tolerance, quantity forecast, and delivery country.
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